1 /*
2  * NOTE: This example is works on x86 and powerpc.
3  * Here's a sample kernel module showing the use of kprobes to dump a
4  * stack trace and selected registers when _do_fork() is called.
5  *
6  * For more information on theory of operation of kprobes, see
7  * Documentation/kprobes.txt
8  *
9  * You will see the trace data in /var/log/messages and on the console
10  * whenever _do_fork() is invoked to create a new process.
11  */
12 
13 #include <linux/kernel.h>
14 #include <linux/module.h>
15 #include <linux/kprobes.h>
16 
17 #define MAX_SYMBOL_LEN	64
18 static char symbol[MAX_SYMBOL_LEN] = "_do_fork";
19 module_param_string(symbol, symbol, sizeof(symbol), 0644);
20 
21 /* For each probe you need to allocate a kprobe structure */
22 static struct kprobe kp = {
23 	.symbol_name	= symbol,
24 };
25 
26 /* kprobe pre_handler: called just before the probed instruction is executed */
27 static int handler_pre(struct kprobe *p, struct pt_regs *regs)
28 {
29 #ifdef CONFIG_X86
30 	pr_info("<%s> pre_handler: p->addr = 0x%p, ip = %lx, flags = 0x%lx\n",
31 		p->symbol_name, p->addr, regs->ip, regs->flags);
32 #endif
33 #ifdef CONFIG_PPC
34 	pr_info("<%s> pre_handler: p->addr = 0x%p, nip = 0x%lx, msr = 0x%lx\n",
35 		p->symbol_name, p->addr, regs->nip, regs->msr);
36 #endif
37 #ifdef CONFIG_MIPS
38 	pr_info("<%s> pre_handler: p->addr = 0x%p, epc = 0x%lx, status = 0x%lx\n",
39 		p->symbol_name, p->addr, regs->cp0_epc, regs->cp0_status);
40 #endif
41 #ifdef CONFIG_ARM64
42 	pr_info("<%s> pre_handler: p->addr = 0x%p, pc = 0x%lx,"
43 			" pstate = 0x%lx\n",
44 		p->symbol_name, p->addr, (long)regs->pc, (long)regs->pstate);
45 #endif
46 #ifdef CONFIG_S390
47 	pr_info("<%s> pre_handler: p->addr, 0x%p, ip = 0x%lx, flags = 0x%lx\n",
48 		p->symbol_name, p->addr, regs->psw.addr, regs->flags);
49 #endif
50 
51 	/* A dump_stack() here will give a stack backtrace */
52 	return 0;
53 }
54 
55 /* kprobe post_handler: called after the probed instruction is executed */
56 static void handler_post(struct kprobe *p, struct pt_regs *regs,
57 				unsigned long flags)
58 {
59 #ifdef CONFIG_X86
60 	pr_info("<%s> post_handler: p->addr = 0x%p, flags = 0x%lx\n",
61 		p->symbol_name, p->addr, regs->flags);
62 #endif
63 #ifdef CONFIG_PPC
64 	pr_info("<%s> post_handler: p->addr = 0x%p, msr = 0x%lx\n",
65 		p->symbol_name, p->addr, regs->msr);
66 #endif
67 #ifdef CONFIG_MIPS
68 	pr_info("<%s> post_handler: p->addr = 0x%p, status = 0x%lx\n",
69 		p->symbol_name, p->addr, regs->cp0_status);
70 #endif
71 #ifdef CONFIG_ARM64
72 	pr_info("<%s> post_handler: p->addr = 0x%p, pstate = 0x%lx\n",
73 		p->symbol_name, p->addr, (long)regs->pstate);
74 #endif
75 #ifdef CONFIG_S390
76 	pr_info("<%s> pre_handler: p->addr, 0x%p, flags = 0x%lx\n",
77 		p->symbol_name, p->addr, regs->flags);
78 #endif
79 }
80 
81 /*
82  * fault_handler: this is called if an exception is generated for any
83  * instruction within the pre- or post-handler, or when Kprobes
84  * single-steps the probed instruction.
85  */
86 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
87 {
88 	pr_info("fault_handler: p->addr = 0x%p, trap #%dn", p->addr, trapnr);
89 	/* Return 0 because we don't handle the fault. */
90 	return 0;
91 }
92 
93 static int __init kprobe_init(void)
94 {
95 	int ret;
96 	kp.pre_handler = handler_pre;
97 	kp.post_handler = handler_post;
98 	kp.fault_handler = handler_fault;
99 
100 	ret = register_kprobe(&kp);
101 	if (ret < 0) {
102 		pr_err("register_kprobe failed, returned %d\n", ret);
103 		return ret;
104 	}
105 	pr_info("Planted kprobe at %p\n", kp.addr);
106 	return 0;
107 }
108 
109 static void __exit kprobe_exit(void)
110 {
111 	unregister_kprobe(&kp);
112 	pr_info("kprobe at %p unregistered\n", kp.addr);
113 }
114 
115 module_init(kprobe_init)
116 module_exit(kprobe_exit)
117 MODULE_LICENSE("GPL");
118